Package org.apache.velocity.runtime.resource.loader

Class DataSourceResourceLoader

java.lang.Object

org.apache.velocity.runtime.resource.loader.ResourceLoader

org.apache.velocity.runtime.resource.loader.DataSourceResourceLoader

public class DataSourceResourceLoader
extends ResourceLoader

This is a simple template file loader that loads templates from a DataSource instead of plain files.

It can be configured with a datasource name, a table name, id column (name), content column (the template body) and a datetime column (for last modification info).

Example configuration snippet for velocity.properties:

 resource.loaders = file, ds

 resource.loader.ds.description = Velocity DataSource Resource Loader 

 resource.loader.ds.class = org.apache.velocity.runtime.resource.loader.DataSourceResourceLoader 

 resource.loader.ds.resource.datasource_url = java:comp/env/jdbc/Velocity 

 resource.loader.ds.resource.table = tb_velocity_template 

 resource.loader.ds.resource.key_column = id_template 

 resource.loader.ds.resource.template_column = template_definition 

 resource.loader.ds.resource.timestamp_column = template_timestamp 

 resource.loader.ds.cache = false 

 resource.loader.ds.modification_check_interval = 60 

 

Optionally, the developer can instantiate the DataSourceResourceLoader and set the DataSource via code in a manner similar to the following:

 DataSourceResourceLoader ds = new DataSourceResourceLoader();
 ds.setDataSource(DATASOURCE);
 Velocity.setProperty("resource.loader.ds.instance",ds);
 

The property resource.loader.ds.class should be left out, otherwise all the other properties in velocity.properties would remain the same.

Example WEB-INF/web.xml:

  <resource-ref>
   <description>Velocity template DataSource</description>
   <res-ref-name>jdbc/Velocity</res-ref-name>
   <res-type>javax.sql.DataSource</res-type>
   <res-auth>Container</res-auth>
  </resource-ref>
 

and Tomcat 4 server.xml file:

  [...]
  <Context path="/exampleVelocity" docBase="exampleVelocity" debug="0">
  [...]
   <ResourceParams name="jdbc/Velocity">
    <parameter>
      <name>driverClassName</name>
      <value>org.hsql.jdbcDriver</value>
    </parameter>
    <parameter>
     <name>driverName</name>
     <value>jdbc:HypersonicSQL:database</value>
    </parameter>
    <parameter>
     <name>user</name>
     <value>database_username</value>
    </parameter>
    <parameter>
     <name>password</name>
     <value>database_password</value>
    </parameter>
   </ResourceParams>
  [...]
  </Context>
  [...]
 

Example sql script:

  CREATE TABLE tb_velocity_template (
    id_template varchar (40) NOT NULL ,
    template_definition text (16) NOT NULL ,
    template_timestamp datetime NOT NULL
  );
 

Since:

1.5

Version:

$Id$

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	DataSourceResourceLoader.SelfCleaningReader

Field Summary

Fields

Modifier and Type	Field	Description
private Connection	connection
private InitialContext	ctx
private DataSource	dataSource
private String	dataSourceName
private String	keyColumn
private String	tableName
private String	templateColumn
private PreparedStatement	templatePrepStatement
private String	timestampColumn
private PreparedStatement	timestampPrepStatement

Fields inherited from class org.apache.velocity.runtime.resource.loader.ResourceLoader

className, isCachingOn, log, modificationCheckInterval, rsvc

Constructor Summary

Constructors

Constructor	Description
DataSourceResourceLoader()

Method Summary

Modifier and Type	Method	Description
private void	checkDBConnection()	Checks the connection is valid
private void	closeDBConnection()	Closes the prepared statements and the connection to the datasource
private void	closeResultSet(ResultSet rs)	Closes the result set.
protected ResultSet	fetchResult(PreparedStatement ps, String templateName)	Fetches the result for a given template name.
protected void	finalize()	Close DB connection on finalization
long	getLastModified(Resource resource)	Get the last modified time of the InputStream source that was used to create the template.
protected Reader	getReader(ResultSet resultSet, String column, String encoding)	Gets a reader from a result set's column
Reader	getResourceReader(String name, String encoding)	Get an InputStream so that the Runtime can build a template with it.
void	init(ExtProperties configuration)	Initialize the template loader with a a resources class.
boolean	isSourceModified(Resource resource)	Given a template, check to see if the source of InputStream has been modified.
private void	openDBConnection()	Gets connection to the datasource specified through the configuration parameters.
protected PreparedStatement	prepareStatement(Connection conn, String columnNames, String tableName, String keyColumn)	Creates the following PreparedStatement query : SELECT columnNames FROM tableName WHERE keyColumn = 'templateName' where keyColumn is a class member set in init()
private long	readLastModified(Resource resource, String operation)	Fetches the last modification time of the resource
void	setDataSource(DataSource dataSource)	Set the DataSource used by this resource loader.

Methods inherited from class org.apache.velocity.runtime.resource.loader.ResourceLoader

buildReader, commonInit, getClassName, getModificationCheckInterval, isCachingOn, resourceExists, setCachingOn, setModificationCheckInterval

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

dataSourceName

private String dataSourceName

tableName

private String tableName

keyColumn

private String keyColumn

templateColumn

private String templateColumn

timestampColumn

private String timestampColumn

ctx

private InitialContext ctx

dataSource

private DataSource dataSource

connection

private Connection connection

templatePrepStatement

private PreparedStatement templatePrepStatement

timestampPrepStatement

private PreparedStatement timestampPrepStatement

Constructor Details

DataSourceResourceLoader

public DataSourceResourceLoader()

Method Details

init

public void init(ExtProperties configuration)

Description copied from class: ResourceLoader

Initialize the template loader with a a resources class.

Specified by:

init in class ResourceLoader

Parameters:

configuration -

See Also:

• ResourceLoader.init(org.apache.velocity.util.ExtProperties)

setDataSource

public void setDataSource(DataSource dataSource)

Set the DataSource used by this resource loader. Call this as an alternative to specifying the data source name via properties.

Parameters:

dataSource - The data source for this ResourceLoader.

isSourceModified

public boolean isSourceModified(Resource resource)

Description copied from class: ResourceLoader

Given a template, check to see if the source of InputStream has been modified.

Specified by:

isSourceModified in class ResourceLoader

Parameters:

resource -

Returns:

True if the resource has been modified.

See Also:

• ResourceLoader.isSourceModified(org.apache.velocity.runtime.resource.Resource)

getLastModified

public long getLastModified(Resource resource)

Description copied from class: ResourceLoader

Get the last modified time of the InputStream source that was used to create the template. We need the template here because we have to extract the name of the template in order to locate the InputStream source.

Specified by:

getLastModified in class ResourceLoader

Parameters:

resource -

Returns:

Time in millis when the resource has been modified.

See Also:

• ResourceLoader.getLastModified(org.apache.velocity.runtime.resource.Resource)

getResourceReader

public Reader getResourceReader(String name,
 String encoding)
                         throws ResourceNotFoundException

Get an InputStream so that the Runtime can build a template with it.

Specified by:

getResourceReader in class ResourceLoader

Parameters:

name - name of template

encoding - asked encoding

Returns:

InputStream containing template

Throws:

ResourceNotFoundException

Since:

2.0

readLastModified

private long readLastModified(Resource resource,
 String operation)

Fetches the last modification time of the resource

Parameters:

resource - Resource object we are finding timestamp of

operation - string for logging, indicating caller's intention

Returns:

timestamp as long

openDBConnection

private void openDBConnection()
                       throws NamingException,
SQLException

Gets connection to the datasource specified through the configuration parameters.

Throws:

NamingException

SQLException

checkDBConnection

private void checkDBConnection()
                        throws NamingException,
SQLException

Checks the connection is valid

Throws:

NamingException

SQLException

finalize

protected void finalize()
                 throws Throwable

Close DB connection on finalization

Overrides:

finalize in class Object

Throws:

Throwable

closeDBConnection

private void closeDBConnection()

Closes the prepared statements and the connection to the datasource

closeResultSet

private void closeResultSet(ResultSet rs)

Closes the result set.

prepareStatement

protected PreparedStatement prepareStatement(Connection conn,
 String columnNames,
 String tableName,
 String keyColumn)
                                      throws SQLException

Creates the following PreparedStatement query :
SELECT columnNames FROM tableName WHERE keyColumn = 'templateName'
where keyColumn is a class member set in init()

Parameters:

conn - connection to datasource

columnNames - columns to fetch from datasource

tableName - table to fetch from

keyColumn - column whose value should match templateName

Returns:

PreparedStatement

Throws:

SQLException

fetchResult

protected ResultSet fetchResult(PreparedStatement ps,
 String templateName)
                         throws SQLException

Fetches the result for a given template name. Inherit this method if there is any calculation to perform on the template name.

Parameters:

ps - target prepared statement

templateName - input template name

Returns:

result set

Throws:

SQLException

getReader

protected Reader getReader(ResultSet resultSet,
 String column,
 String encoding)
                    throws SQLException

Gets a reader from a result set's column

Parameters:

resultSet -

column -

encoding -

Returns:

reader

Throws:

SQLException